Detailed description design and operating principle, recommendations for use and installation methods, calorimetric flow sensors manufactured by EGE-Elektronik.
All about calorimetric sensors
Operating principle of calorimetric flow sensors
The operation of the sensors is based on the thermodynamic principle of operation. The measuring probe of the sensor is forced (from the inside) to heat up several degrees above the temperature of the medium (liquid flow) in which it is immersed. In the presence of a flow, the heat generated in the probe is removed by the flow of the medium, thus cooling the probe. The temperature established in the probe is measured and compared with the temperature of the controlled environment. In this case, the measured temperature difference is proportional to the flow speed, and, consequently, to the flow rate (flow rate) of the measured medium.
Sensor sensitivity and medium temperature
The sensitivity of thermodynamic sensors depends on the thermal properties of the measured medium. Thus, the sensitivity of a standard sensor due to lower thermal conductivity, for oil, for example, should be 3 times, and for air 30 times higher than for water. Thermodynamic flow sensors operate without moving parts, so there is no risk of bearing corrosion, impeller fracture or deformation of fairings. This circumstance determined their high reliability, which is highly valued in all industries.
Control in cooling systems
- The parameters of the flow of cooling water in welding installations are controlled using compact instruments, the sensitive elements of which are made of stainless steel. At the same time, the necessary cooling is ensured even at high rates of welding operations. If the cooling system fails, the welding robot automatically switches off.
- To protect metal-cutting tools and extend their service life, the flow of coolants in metalworking centers is continuously monitored.
- Rolls of rolling mills and rollers in drawing machines must be constantly cooled. This process is also controlled by thermodynamic sensors, which can also be used at extreme – up to + 160ºC – ambient temperatures. In this case, regulation of the required parameters is provided remotely by special devices installed under normal operating conditions.
Control of liquid media transportation
- Dry-running protection of various pumps is a common application for compact sensors with built-in switch-off delay functions.
- In dosing technology, controlling the flow of metered materials is of great importance. The passage of even the smallest doses can be sensed using flow sensors. In this case, sensors are built directly into the pipeline as part of its section.
- Clogging of various types of filtering and screening installations can also be carried out using flow control. When the flow characteristics reach the limit values, a signal is issued to replace the filter material. If replacement does not occur, the pump is switched off in the next stage of the process to avoid dry running. To solve this problem, sensors with two actuation points are used
Process control
- Monitoring the progress of various types of cleaning or rinsing processes, including those using aggressive media, can be provided by sensors made of special materials such as Hastelloy alloy or tantalum.
- The operation of devices for extracting vapors hazardous to human health from workplaces in laboratories, as well as ventilation systems for premises in industries processing hexane, is controlled using air flow sensors.
- Flow sensors can also be used to monitor and document the cleaning and sterilization processes of equipment on site.
Design, installation of sensors and materials for their manufacture
Design Features
At the tip of the sensor pin there is a temperature-dependent measuring element. The measuring tip and the fastening part with a thread cut on it are one piece and, for many sensors, are made of stainless steel. This achieves absolute tightness and high resistance to excess pressure. For corrosive, especially oxidizing, measured media, special materials are used, since stainless steel is only conditionally resistant to them.
In standard use, the method of mounting the sensors may not depend on the direction of movement of the measured medium.
It is fundamentally important to ensure that the sensor pin is completely immersed in it in each case. It must be taken into account that the tip of the sensor reduces the cross-section of the pipe in which it is installed. For small diameters this causes an increase in flow rate. In order to avoid disturbances in the operation of the sensor that arise due to instability of the dynamic characteristics of the flow, it is not allowed to install directly, closer than 4...8 pipe diameters, before or after the sensor, any devices that affect their quality.
Measuring sensors of STK... versions with short thread are intended for installation only on tees. Their mounting length is determined in such a way that the tip of the sensor is completely surrounded by the measuring medium, while touching the opposite wall of the pipeline. Measuring sensors of ST... versions with long thread are designed for large diameter pipes or for connection via long threaded fittings. All standard sensor threads are G-type cylindrical pipe threads in accordance with the international standard DIN ISO 228 and comply with BSP (British standard pipe thread).
Methods for installing submersible sensors
Installation in a vertical pipeline
Using this method, flow meters are mounted in open systems with possible air inclusions.
Installation in a horizontal pipeline
With side mounting, neither air cushions nor sediment cause measurement errors if the sensor is completely immersed in the medium being measured.
Installation from below (horizontal pipeline)
The installation from below also guarantees that the measuring function can be carried out even if there is air in the pipe. However, the level of the medium being measured must not be below the top edge of the sensor sensing element. Installation from above is only possible if the pipeline is completely filled and there are no gas or air inclusions.
Seal
Flat gaskets, fluoroplastic sealing tapes or liquid sealing materials can be used for sealing. At pressures above 30 bar or high tightening torques, flat non-metallic gaskets can be damaged. In such cases, it is necessary to make a recess in the pipeline wall to prevent the gasket from distorting under the influence of high loads. For fluoroplastic gaskets, this technology is recommended in all cases. For high pressures, metal gaskets are used. Each measuring sensor is supplied with a gasket made of AFM 34. Special purpose gaskets made of other materials, such as copper or fluoroplastic, are available on request.
Process connection
As an alternative to G-type cylindrical pipe threads, tapered NPT threads can be used in the manufacture of flow meters of all types. There are two types of such threads. NPT threads comply with the international standard ANSI B 1.20.1, are not self-sealing and require the use of a sealing material such as PTFE tape. The use of this type of flat gaskets with threads is not permitted. NPTF threads comply with the international standard ANSI B 1.20.3, are self-sealing and do not require the use of additional seals. When using a thread of this type, it is necessary to take into account that the materials from which the sensor is made and the pipeline part into which it is screwed match in hardness. This prevents the threads from breaking. Without special request, the sensor is threaded NPT type without self-sealing.
Flange connections
The specifics of such industries as chemistry, pharmaceuticals and food industry require the use of standardized pipe connections. Flow meters for these industries are supplied with mating flanges in accordance with DIN or ASME standards. The flange is welded to the sensor using corrosion-resistant methods such as laser or argon welding.
Typical connections in the food industry
For reasons of hygiene, the use of flow meters in the food and pharmaceutical industries places special demands on them, both mechanically and electronic components. Sensors with Triclamp connections comply with Section 3-A of Sanitary Standard 28-03. Periodic cleaning and disinfection processes technological equipment, due to temperature changes, impose an additional load on the electronic elements of the sensors, which requires additional measures for their protection. The materials from which sensors for these industries are made are mainly stainless steel types 1.4404 and 1.4435. Upon customer request, connecting elements such as, for example, Varivent valves from GEA or APV flanges can be supplied.
Extended sensor connections
Flow sensors are available with screw-in lengths from 25 to 300 mm. For use in hazardous areas ah, starting from a length of 110 mm, they consist of two parts, connected to each other by corrosion-resistant laser welding. The length of the flow meter must be selected so that the tip of the pin is located in an area with stable dynamic characteristics of fluid flow.
Extended sensor designs are required in the following cases:
- when measuring the characteristics of low-velocity flows in large-diameter pipes;
- when installing sensors using standard threaded flanges;
- when installing sensors using extended welded couplings for pipelines with insulating coating.
The variable L value is determined from the tip of the pin and includes the thickness of the spacer. Standard lengths for standard sensors are 80 and 120 mm, for explosion-proof ones - 80, 110, 140 mm.
Connections for flow sensors (inline)
Flow sensors are built directly into the pipeline line. This design does not contain any immersed measuring probes. Flow sensors manufactured by EGE-Electronic 500 series are designed to measure liquid flow in the range from 0.5 ml/min to 6 l/min. Sensors of this type are characterized by a smooth measuring tube, low pressure loss in the flow and fast response to changes in its characteristics. The consumer is given a wide choice various options to connect them to the process.
Materials used to make sensors
Chemical resistance of measuring sensor housings
The chemical resistance of the materials used must be checked on a case-by-case basis. There will be no problems if the sensor and the pipeline on which it is installed are made of the same material. It is even more practical to make the sensor from a more resistant material.
Cable sockets for ST... sensors are made of nickel-plated brass. For applications that use highly alkaline detergents, in the manufacture of cable sockets it is preferable to use polyvinylidene fluoride (PVDF).
Stainless steels belong to the group of chromium-nickel alloys with additional alloying additives such as molybdenum or titanium. The combination of various alloying additives determines the corrosion resistance of the material in the environment. Therefore, stainless steels contain a large number of alloying components, the content of which is indicated in their grade in accordance with the international standard DIN EN ISO 7153-1. Stainless steel 1.4571(VA4), due to its corrosion resistance, is used in many industries. It is used in water supply, climate control systems, meat and fish processing, beverage production, winemaking and cooking. At the same time, stainless steels are only conditionally resistant to chlorine-containing or oxygen-poor environments. This requires the use of special alloys.
Special materials
Hastelloy B2(2.4617) belongs to the group of highly corrosion-resistant nickel-molybdenum alloys. This material is characterized by high resistance in environments with low oxygen content, such as hydrochloric acid over a full range of concentrations and a wide temperature range. It is also applicable to hydrogen chloride, sulfuric, acetic and fluoric acids. Good resistance to pitting and crevice corrosion, corrosion cracking caused by chloride compounds, corrosion from various types of scratches and delamination, and temperature corrosion expands its scope of application. Its use in environments containing iron and copper-based salts is not recommended.
Hastelloy C-22(2.4602) belongs to the group of highly corrosion-resistant nickel-chromium-molybdenum-tungsten alloys. This material is characterized by high resistance to pitting and crevice corrosion, corrosion cracking in acidic and oxygen-depleted environments. The material exhibits good resistance to a large number of aggressive environments, including oxidizing agents such as iron and copper chlorides, hot environments, sulfuric, nitric, phosphoric, acetic and formic acids, dry chlorine. In addition, it has good resistance to wet chlorine gas, sodium hypochloride and chlorine dioxide.
Titanium(3.7035) is a lightweight metal whose strength is equal to that of the best structural steels. The chemical resistance of this metal is ensured by the formation of a persistent oxide film on its surface, as happens with stainless steels. In case of mechanical damage to this layer, it is formed again under the influence of oxygen. Titanium is even resistant to aqua regia. In a completely oxygen-free or slightly acidic environment, titanium is unstable. Titanium exhibits its properties especially well in environments containing chlorides. Experience in the use of titanium in the chemical and paper industries shows that it is the only material that guarantees trouble-free production. The exceptional properties of titanium also provide optimal results when used in seawater cooling systems and desalination plants. The material, along with other metals and metal-ceramic materials, is part of the B3 lining, which increases the chemical resistance and, at the same time, the service life of sensor housings.
Chemical resistance of lining B3*
Environment/persistence
Cl 2 / +++
HCl (25%) / +++
Br 2 / +++
HBr (20%) / +++
F 2 / +
HF (15%) / +
HA** / +++
NaOH/++
Salt water*** / +++
Slightly acidic environments / ++
HNO 3 (30%) / ++
H 2 SO 4 (25%) / +++
Notes:
* — The coating is hard, wear-resistant and resistant to abrasives such as chalk, mud, sand or glass wool. The stability of the coating relative to the materials indicated in the table is reliable at temperatures up to 30 ºC.
** - Resistance to acetic acid valid for the full concentration range.
*** - Resistance to salt water was tested using a climate test (Kesternich test).
High temperature resistance
High temperature flow sensors are manufactured from temperature resistant materials and are installed on fluoropolymer insulated pipelines. The operating temperature range of the special 400 series sensors is from + 10 to + 120 ºC. In this case, a short-term temperature increase of up to 135ºC, no more than 10 minutes, is allowed. High-temperature flow sensors of the 500 series can be used at temperatures up to 160ºC.
Explosion-proof sensors
Sensors to be used in explosive gas and dust areas are certified for compliance with European requirements for the operation of equipment in potentially explosive atmospheres ATEX 100a/ATEX95 and are used in conjunction with the corresponding secondary devices of the SZA, SEA or SS400 series from the EGE range. Depending on the approval category, operation of the sensors is permitted in the appropriate zones: 0.1 or 2 for gas; 20, 21 or 22 - for dusty environments. As standard material Stainless steel 1.4571 is used for the manufacture of explosion-proof flow sensors. Other stainless steels and alloys can also be used upon special request, including Hastelloy, Monel and some bronzes. When choosing a material for manufacturing, its resistance to corrosion is taken into account.
Electrical connection
The sensors are supplied either with a four-pin M12 plug connector or with a four-wire cable section that is rigidly attached and routed outwards. The length of the cable connecting the sensor to the secondary device should not exceed 100 m. When the sensor is removed from the device at a distance of more than 30 m and in areas with high level To avoid various types of interference, shielded cable must be used. In each case, it is necessary to ensure that the selected cable cross-section corresponds to the application conditions.
Secondary devices and compact sensors
Secondary devices
Devices of the SKZ…/SKM… series are designed for mounting on a support rail. They process signals coming from sensors and generate output analog and relay signals. The devices are configured using two potentiometers located on the front panel or, in the SRM 522 device, the corresponding keys. A multi-color LED strip indicates the flow status of the medium being measured. Devices of the SKZ series additionally provide response delay of control output channels and temperature control. When installing devices, it must be taken into account that they should not be exposed to heat. The distance between two devices installed next to each other must be at least 10 mm.
Ex - devices
Devices of the SEA…/SZA… series are designed for processing signals from explosion-proof sensors. They include the sensor in an individually isolated electrical circuit, which is galvanically isolated from the electrical power circuits, as well as the output of analog and relay signals. All Ex devices, without taking into account additional protective measures for hazardous areas, must have a protection class of at least IP 20 in accordance with standard EN 60529. Additional equipment for such devices requires either the installation of a dividing wall between insulated and non-insulated connections so that the distance between them is at least 50 mm, or sealing each contact connection in a special non-slip heat-shrinkable casing. As an alternative, the use of crimping technology is allowed.
LED - lines (LED lines)
All devices are equipped with a multi-color LED bar that visually displays changes in flow characteristics. The red LED lights up to indicate that the flow rate has not reached the set value and there is no output signal. The yellow LED indicates that the flow rate has reached the set value and the output signal is turned on. Four green LEDs can, in addition to the yellow one, indicate the relative extent of the flow rate exceeding the set point.
Compact sensors
Compact sensors combine the functions of a measuring sensor and a secondary device in one housing, which makes it possible to set specified values directly at the measurement location. In order to reduce the influence of various types of interference on measurement results and output control signals, the length of the cable for remote signal transmission is limited.
Sensors modifications SN…/ LN…
The devices of the SC 440 series are housed in a stainless steel housing. Their service life in industrial conditions is at least 20 years. They are compact, reliable and come in two versions: screw-in and plug-in. The compact devices of the SN 450 / LN 450 series are offered in a housing made of artificial material. Their design varies depending on electrical characteristics such as power supply (DC or AC) and type of output signals (PNP output, relay output, analog output). There are also special designs that provide control of temperature limit values or delay the response time of control channels.
SDN series compact flow sensors/SDNC
Flow (inline) compact sensors of the SDN series
Sensors of the SDN 500... series are built “in-line”, directly into the pipeline. Their measuring tube is smooth inside and does not have any parts protruding into the flow. They are characterized by short reaction times and a wide measuring range. Thanks to their small size, they can be installed in places with limited installation space. Sensors in this series are equipped with PNP outputs, as well as relay and analog outputs. They even recognize small pulsating currents.
SDNC series compact flow sensors
The SDNC 503 series devices are characterized by their compact size cubic shape, a wide measurement range and are installed using a screw-in adapter, creating an efficient flow profile for flow measurement. Devices in this series are supplied completely ready for installation, are used for measuring the flow of water and aqueous solutions and have a pulse output convenient for flow metering.
Parameters for selecting flow sensors
Detection range
The detection range determines the flow rates for which the sensor can generate an evaluable signal. If the measurement medium is not specified when ordering, all sensor characteristics are indicated based on the aquatic environment. Since different media have different thermal conductivity, their detection range and temperature drift are also different. In this case, the temperature drift values take higher values at the lower and upper limits of the detection range. The detection range does not limit the maximum flow rate that the sensor can be used to measure. For example, a sensor with an upper detection limit of 3 m/s can be installed in a flow with a speed of 10 m/s.
Operating range
The operating range denotes the part of the detection range in which the flow characteristics of the sensor are established or, in other words, defines its measurement scale. In other sectors of the detection range, these characteristics may be unreliable and the sensor output signals will not correspond to the flow rate.
Maximum flow
All specifications of each sensor are determined relative to the rated maximum flow that it can reliably measure. This is necessary because the output characteristic of the sensor is nonlinear. Consequently, the correspondence of the signal value generated by the sensor to a certain flow speed is established by its location on the operating curve of the line. As a rule, nominal flow rates are located in the linear part of the graph, described using the natural logarithm function. For this operating point, the corresponding values for the on, off, and readiness times are determined, as well as the hysteresis and temperature gradient.
Supply voltage
The supply voltage must be within the voltage range in which the sensors operate reliably. When powering the sensors with voltage direct current It must be taken into account that the range limits are set taking into account the residual ripple.
Current consumption
Current consumption is the maximum current consumed by the sensor without external load.
Switching current
Switched current is the maximum value of current that the sensor output channels can switch over a long period of time. For PNP outputs, this value is valid at an ambient temperature of no higher than 25º C. Increasing the temperature reduces the maximum current value. For devices with relay outputs, this value depends on the category of use (AC-12 or DC-12) according to EN 60947-5-1.
Switching voltage
Switching voltage is the maximum voltage, including residual ripple, that the relay outputs can switch.
Switching power
Switched power is the maximum power that the relay outputs can switch.
Ambient temperature
This parameter sets the minimum and maximum ambient temperature values permissible for sensor operation.
Temperature of the measured medium
This parameter sets the minimum and maximum temperature value of the measured medium permissible for operation of the sensor.
Temperature gradient
This parameter sets the maximum value of change in ambient temperature per unit time that does not affect the operation of the sensor. Changes in temperature at a rate exceeding this value can lead to malfunctions.
Ready time
This is the time after power supply required for the sensor to transition to a stable operating state. After this time, the sensor can either be configured or be able to generate a reliable signal. Before power is applied, the flow rate must be within the operating range and the temperature of the sensor body must be equal to the temperature of the medium being measured.
Reaction time
The response time consists of the turn-on time and the turn-off time of the output signal. The switch-on time is the time elapsed from the moment the flow rate reaches the set value until the flow status is indicated. This time is minimal at low flow rates and increases as the flow rate increases. The shutdown time is the time elapsed from the moment the flow rate drops below the set value until the flow status is indicated. This time is minimal at high flow rates and increases as it decreases.
Pressure resistance
Pressure resistance depends on the strength of the sensor housing. If the pressure of the measured medium does not exceed the specified maximum value, the sensor generates a stable signal and its housing is not damaged. The pressure resistance of sensors with a screw-in design may be lower than indicated in their technical data, so their use at pressures close to the maximum should be avoided.
Protection class
The protection class specifies the degree of protection of the sensor against the penetration of solids and water in accordance with the EN 60529 standard. For sensors, the protection class depends on the location and method of installation. Sensors in direct contact with the measuring medium always have a degree of protection corresponding to class IP 68.
On delay time
This variable can be set from 0 to 25 s and causes a delay in issuing control output signals when the flow rate deviates from the set values. For example. If a non-zero delay time is set, the control output is still turned on at that moment, although the flow rate has already fallen below the set value. In other words, the red LED (“No flow”) and yellow (“Output activated”) light up simultaneously. After the delay time has expired, the yellow LED goes out and only the red LED lights up.
Immersion sensors and flow switches
Fast, highly accurate and wear-free immersion type flow sensors for flow monitoring and liquid flow measurement with analogue, transistor or relay outputs
Sensors and pressure switches for gases, vapors and liquids with analogue output 4...20mA and discrete outputs with programmable warning limits.
I found the right thing to solve my problem. The tasks are:1) In order for the garden watering to work or to be able to wash the car (in this case, the “pump blocking” should not be triggered if the upper pressure is NOT set for a certain time, if it is specified in the operating algorithm)
2) Have a timer to turn off after closing the flow - shutting off the tap, airing the cold water, blocking, etc. (In the case of the dry running relay, the question was asked - “What if the pump reaches an upper pressure of 2.2 instead of the required 3.2 bar when air enters the line and the relay does not seeing the lower shutdown pressure will not turn off the pump?" Therefore need a timer to turn off the pump after interruption of flow)
3) The flow sensor makes it possible to pump pressure into the RB. (RB is necessary for water hammer and for water supply, as well as for “activating” the flow sensor, which will start the pump immediately or according to a timer or lower pressure)
4) The unit should not cost too much money, since manufacturers do not have a great desire to provide warranty repairs, spare parts should also be reasonably priced.
5) The device can be restarted from a button or from a plug (socket with a switch) without having to run to the basement to restart the pump when the lights are turned off.
6) When the cold water becomes airy, the flow sensor turns off the pump (in the case of watering the garden, the timer will work after the flow disappears).Judging by the points, UNIPUMP TURBI-M1 suits me, I think it can work in conjunction with a pressure switch and here are the options for action.
I connect the wires: pressure switch + turbo m-1 + pump with RB.
At first start, pressure = 0 bar. I pour water into the system (pump, flow switch, etc.) and open the valve to release air. The pressure switch transmits electricity to the M-1 turbine, and the M-1 turbine, upon first start-up (during reboot), transmits power to the engine.If I water the garden, the pump works constantly (if the upper pressure is not reached, it will not turn off the power to the pressure switch, and the flow sensor will NOT turn off the electricity, since there is a flow). In the case when all taps are closed = no flow, pressure is built up in the RB, the pump will turn off by breaking the circuit in the event of an upper threshold from the pressure switch command, or the pump will turn off the flow sensor according to the timer, whichever works first. It would probably be better to select the upper pressure so that the power to the pressure switch is turned off earlier, well, this is just a thought for now.
If the power to the pressure switch is turned off, the flow sensor is also de-energized. This means that when the pressure drops below lower limit, let’s say for a pressure switch it will be 1.8 bar, it supplies power to the flow sensor. The flow sensor (in theory), when turned on/restarted, should see this pressure and operate (SUPPLY VOLTAGE TO THE PUMP) ONLY when it reaches its minimum pressure of 1.5 bar or along the flow.
This is in theory.
Further. The pressure drops (when the tap is opened) below 1.5 bar - the pump turns on at the command of the flow sensor and again everything goes in a circle.If the light is turned off, then WHEN there is the required pressure in the cold water, the relay does not turn on the pump and the flow sensor does not turn on the pump, since there is no flow. And if the lights were turned off and I relieved the pressure in the cold water supply to zero - I wanted to get some water, then this system can only be started by rebooting the flow sensor, but in fact, after turning on the light, the flow sensor should turn on itself (like the pressure switch) - in fact, this restart is there.
If air leaks from the well, but the pressure switch continues to pump pressure to the upper set limit, the flow sensor will turn off the power to the pump by timer. (If there is no flow and low pressure, the flow sensor turns off the pump after 30 seconds.)
In principle, according to theory, everything works out smoothly. If I missed something, please fill me in.
Since the flow sensor works from two moments: when the lower threshold of 1.5 bar is reached or When a flow appears, I think the presence of a pressure switch will reduce the frequency of turning on the pump, so as not to run the pump every time the tap is opened.Z.Y. Before buying a thing, you have to run options for working and try it out based on theory or people’s experience.
Information on the flow sensor.
In modern technology, the water level sensor performs the function of one of the human senses. The proper operation of the entire mechanism depends on how correctly it is possible to manage and control the state of the water flow. The importance of the reliability of the sensor device is difficult to overestimate, if only because the device that controls water, as a rule, becomes the very “narrow” link of modern technology.
Design and principle of operation
Regardless of what principle of operation is the basis of the device, whether it operates only in signaling mode or simultaneously performs the functions of a watchman, automatic machine or control mechanism, the design of the device always consists of three main components:
- A sensing element capable of responding to the characteristics of the water flow. For example, the actual presence of water, the height of the column or level in the tank, the fact of the movement of water flow in a pipe or line;
- A ballast element that balances the sensor part of the sensor. Without ballast, the sensitive sensor would be triggered by the slightest shock or stray drop of water;
- The transmitting or actuating part that converts the signal from the sensor built into the water sensor into a specific signal or action.
Approximately 90% of all water equipment is, in one way or another, connected to electrical actuators - pumps, valves, heaters and electronic control machines. It is clear that such a device working with water flows must first of all be safe.
Of all the alarm systems, the sensor that monitors the state of water is considered the simplest and most accessible to set up and repair. Unlike sensors and devices that work with temperature, pressure or flow measurements, a water sensor is very easy to control using simple devices, or, in extreme cases, see the level or pumped flow with your own eyes.
Types of level sensors
One of the conditions successful work sensor is the high sensitivity of the sensor, the higher the better, the more accurately it is possible to read the controlled water parameter. Therefore, as the quantity measured by the sensor, they try to choose the one that changes the most during the measurement time.
Today there are about two dozen in various ways and measurement methods mechanical characteristics water, but they are all used to obtain information:
- The height of the water column in the container or tank;
- The speed of flow or flow of water;
- The fact of the presence or absence of water in a closed container, reservoir, pipe or heat exchanger.
Of course, industrial sensors can be quite complex in design, but the operating principles used in them are the same as in household, gardening or automotive equipment.
Float type overflow sensor
The simplest way to measure water level is using a simple mechanical design consisting of a sealed float, a swinging lever or rocker and shut-off valve. In this case, the sensor is the float, the ballast is the spring and the float weight, and the valve itself is the actuator.
In all float systems, the sensor or float is adjusted to a specific actuation height. The water rising in the tank to the control level raises the float and opens the valve.
The float system can be equipped with an electrical actuator. For example, a magnet insert is installed inside a float sensor; when the water rises to the operating level, the magnetic field causes the vacuum reed switch to close the contacts, and thereby turns on or off the electrical circuit.
The float sensor can also be made according to a free design, as, for example, in submersible pumps. In this case, the reed switch does not close under the influence of the magnetic field of the liner, but only due to the pressure difference inside the pump housing and at the level of the float. Today, a magnetic float sensor with an electric actuator relay is considered one of the safest and most reliable options for monitoring liquid levels.
Ultrasonic sensor
The design of the water sensor provides for the presence of two devices - an ultrasound source and a signal receiver. The sound wave is directed to the surface of the water, reflected and returned to the sensor receiver.
At first glance, the idea of using ultrasound to make a sensor for controlling the level or speed of water does not look very good. An ultrasonic wave can be reflected from the walls of the tank, refracted and interfere with the operation of the receiving sensor, and in addition, complex electronic equipment will be required.
In fact, an ultrasonic sensor for measuring the level of water or any other liquid is placed in a box slightly larger than a pack of cigarettes, and using ultrasound as a sensor provides certain advantages:
- The ability to measure the level and even the speed of water at any temperature, in conditions of vibration or movement;
- The ultrasonic sensor can measure the distance from the sensor to the water surface even in heavily polluted conditions with variable liquid levels.
In addition, the sensor can measure water levels located at significant depths, with measurement accuracy reaching 1-2 cm for every 10 m of height.
Electrode principle of water control
The fact that water is electrically conductive has been successfully used to make contact liquid level sensors. Structurally, the system consists of several electrodes installed in a container at different heights and connected into one electrical circuit.
As the container is filled with water, the liquid sequentially closes a pair of contacts, which turns on the pump control relay circuit. As a rule, the water sensor has two or three electrodes, so the measurement of water flow is too differentiated. The sensor only signals when the minimum level is reached and starts the pump motor, or when the tank is completely filled and turns it off, so such systems are used to control reserve or irrigation water tanks.
Capacitive type water sensor
The condenser or capacitive type of sensor is used to measure the water level in narrow and deep containers, this can be a well or a borehole. Using a capacitive sensor, you can determine the height of the water column in a well with an accuracy of ten centimeters.
The sensor design consists of two coaxial electrodes, actually a pipe and an internal metal electrode, immersed in the wellbore. Water fills part of the internal space of the system, thereby changing its capacity. Using a connected electronic circuit and a quartz oscillation coil, you can accurately determine the sensor's capacitance and the amount of water in the well.
Radar meter
A wave or radar sensor is used to work in the most difficult conditions, for example, if you need to measure the level or volume of liquid in a tank, an open reservoir, or an asymmetrical and irregularly shaped well.
The principle of operation is no different from an ultrasonic device, and the use of an electrical pulse makes it possible to perform measurements with great accuracy.
Hydrostatic sensor option
One of the options for a hydrostatic sensor is shown in the diagram.
For your information! A similar sensor is used in washing machines and boilers, where it is very important to control the height of the water column inside the tank.
The hydrostatic sensor is a box with an elastic spring-loaded membrane that divides the sensor body into two compartments. One of the sections is connected by a durable polyethylene tube to a fitting soldered into the bottom of the tank.
The pressure of the water column is transmitted through the tube to the membrane and causes the contacts of the starting relay to close; most often, a pair is used to start the actuator - a magnetic insert and a reed switch.
Water pressure sensor
Hydrostatic pressure is determined under conditions where a flow or a certain volume of water is at rest. Most often, a hydrostatic sensor is used in heating and heating devices - boilers, heating boilers.
Water pressure sensor device
Such devices most often operate in trigger mode:
- At high blood pressure the water sensor closes the relay contacts and allows the pump or heater to operate;
- At low pressure The sensor even blocks the physical ability to turn on the actuator, that is, no shocks or temporary surges in pressure will make the device work.
If the water pressure sensor is working properly, the sensor will give a signal to start the motor only if the load on the bellows remains for more than three seconds.
A typical smart sensor device is shown in the diagram.
The sensitive element of the system is a diaphragm connected to a bellows; the central rod can rise and fall depending on the pressure, and thereby change the capacity of the built-in capacitor.
Connecting the water pressure sensor
A simplified model of the sensor is used in home systems “hydraulic accumulator - well pump”. Inside the device there is a box with a membrane connected to a swing arm and two balancing springs.
The design is screwed onto the outlet fitting of the hydraulic accumulator. With an increase in internal pressure, the membrane rises and opens the main pair of contacts, so that the system responds properly to water pressure, the moment of turning off and turning on must be adjusted by the settling of the small and large springs in accordance with the readings of the dial pressure gauge.
Water leakage sensor
Already from the name it becomes clear that we are talking about a device that detects the presence of water leaks from water supply lines. The operating principle of the device resembles an electrode system. Inside the plastic box, one or more pairs of electrodes are installed in a special pocket. In the event of an accident, water accumulating on the floor flows into the pocket and closes the contacts. Triggered electronic circuit, and based on the sensor signal, electric ball valves come into operation.
It is clear that the sensor itself is useless if it is used without a control system and automatic water shutoffs installed at the entrance to the house or on one of the water supply branches.
As an example, one of the most popular protection systems is the Neptune water leak sensor. The system includes three main blocks:
- The Neptune leak sensor itself is available in a wired or wireless version; the kit usually includes three separate sensors;
- Ball valve with electric drive, produced by the Italian company Bugatti, two pieces;
- Control unit "Neptune Base".
The most valuable part of the kit is the automatic taps; they are produced for installation on half-inch and inch pipe threads. The design can withstand pressure up to 40 Atm., and the Italian quality of the drive guarantees at least 100 thousand opening-closing cycles.
The sensor itself looks like two brass plates in a box, to which a low voltage voltage is applied with a very high input resistance; when the sensor is shorted, the current is limited to 50 mA. The design itself is made according to the IP67 protocol, therefore it is absolutely safe for humans.
Installation of wireless water leakage sensors
In the Neptune system, the sensor can be removed from the control unit at a distance of more than 50 m. In more advanced NEPTUN PROW+ wireless systems, water leakage sensors equipped with a WF module are used instead of a wire system.
The control unit is equipped with a channel protected from interference and moisture, and an on/off system for ball valves. It is believed that no interference or random drops of moisture or condensation affect the operation of the sensors.
Boxes with a leakage sensor are installed at a distance of no more than 2 m from the pipes; the sensors cannot be shielded by metal plumbing fixtures or furniture.
Wireless water leak sensor
The design of a wireless meter is more complex than a conventional two-electrode version with a wired connection. There is a controller installed inside that continuously compares the current flowing between the electrodes with a reference value stored in memory. In this case, the reference value “dry floor” can be adjusted according to your own choice.
A very convenient solution, considering that the humidity level in the bathroom can be very high, and regularly occurring condensation can lead to false alarms.
As soon as the controller determines the level corresponding to flooding, the water control device sends an alarm signal to the base unit. The most advanced models are capable of duplicating a command via SMS message via GSM channel.
Water flow sensor
In many cases, for stable and trouble-free operation of equipment, a sensor for the presence of water is not enough; information is required about whether the flow is moving through the pipeline, what its speed and pressure are. For these purposes, water flow sensors are used.
Types of water flow sensors
In household and most simple industrial equipment, four main types of flow sensors are used:
- Pressure meter;
- Petal type sensor;
- Blade measurement scheme;
- Ultrasound system.
An outdated pitot tube design is sometimes used, but for reliable operation it requires at a minimum the absence of contamination and laminar water flow. The first three sensors are mechanical, so they are often subject to clogging or water erosion of the sensing element. The latest type of sensor, ultrasonic, is capable of operating in almost any environment.
The operating principle of an ultrasonic meter can be understood from the diagram. Inside the tube there is a wave emitter and a receiver. Depending on the flow speed, the sound wave may deviate from its original direction, which serves as the basis for measuring the flow characteristics.
Design and principle of operation
The simplest petal flow sensors work on the principle of a rowing oar. A petal suspended on a hinge is immersed in the flow. The higher the flow speed, the more the sensor lobe deflects.
More accurate vane sensors use an impeller or turbine made of polyamide or aluminum alloy. In this case, it is possible to measure the flow speed by the rotation frequency of the moving element. The only drawback is the increased resistance created by the petals and blades in the water flow.
The pressure sensor operates using dynamic flow pressure. Under the pressure of water, the movable element with a magnetic liner is squeezed upward, thereby freeing up space for the movement of liquid. The reed switch installed in the head instantly reacts to the magnetic field of the liner and closes the circuit.
Application area
Water flow sensors are used exclusively in heating systems and automation systems of single-circuit heat exchangers. Most often, failure of the flow sensor leads to burnout and severe damage to hot radiators and heaters.
DIY water level sensor
The simplest version of a device capable of signaling the filling of a tank or any other container with water is shown in the diagram below.
Structurally, the level detector consists of three metal electrodes mounted on a textolite plate. The circuit, assembled on a conventional low-power transistor, allows you to determine the maximum permissible upper and lower water levels in the container.
The design is absolutely safe to use and does not require any expensive parts or control devices.
Conclusion
Water level sensors are widely used in household appliances, therefore, most often for auxiliary needs of garage or garden equipment they use already ready-made designs from old equipment, reworked and adapted to new conditions. If connected correctly, such a device will last much longer than a homemade circuit.
One of the common causes of breakdowns of circulation pumps is the so-called “dry running”, when the pump continues to work, but water does not pass through it. This type of work creates danger. emergency situations, when running dry, the engine overheats, parts are deformed, and the pump as a whole wears out quickly. To avoid this problem, manufacturers offer booster and circulation pumps with a flow sensor.
Why do you need a flow sensor?
A flow sensor is a device that determines the movement or stop of the flow of the working fluid in the system to turn the circulation pump on and off. Today, models are produced with both built-in and external sensors. They not only perform the function of protecting the pump, but also ensure the maintenance of optimal pressure in water supply and heating systems.
The principle of operation of the sensor is that it monitors the power of water flow and starts the pump when the water flow rate reaches 1.5 liters per minute, when the speed drops below the set value, the sensor turns off the pump.
Thus, it provides several advantages at once:
- allows the pump to operate in automatic mode;
- allows you to avoid running the pump “dry”, since it starts the system and raises the pressure in it only when necessary;
- automatic switching on and off makes the pump much more economical, reducing energy costs.
The cost of models with a sensor is slightly higher than that of conventional pumps, but they are reliably protected from breakdowns, more reliable and durable.
Liquid flow sensors are designed to indicate the flow of a liquid substance, determine the speed and measure the level of product flow.
Modern flow switches are highly sensitive and are able to respond even to low fluid flow in the pipeline. The variety of models allows the use of flow sensors for working with various types of liquid products, including aggressive and hazardous substances. Some manufacturers offer explosion-proof options that are safe for use in hazardous industries.
Field of application of liquid flow sensors
Fluid flow switches are used to solve various problems in many industries:
- in water supply and wastewater systems to control water supply and maintain operation pumping equipment, organization of drainage systems Wastewater, sewerage structures, protection of pumping equipment and engines from “dry running”,
- in heating, cooling, ventilation and air conditioning systems to control the supply of water, refrigerant, special liquids, removal of waste liquids from the system,
- in the oil and gas sector to control the flow of gas, oil, petroleum products during transportation and storage,
- in metallurgy, steel industry in systems for supplying and discharging water and other liquids,
- in the chemical industry for working with aggressive and dangerous types of liquid products, water supply and drainage systems,
- in agriculture when automating feeding processes, in drinking bowls, in watering and irrigation systems, when working with liquid fertilizers,
- in the food industry for feed control various types liquid food products, including mineral water, dairy and fermented milk products, alcoholic beverages, beer, etc.
Some types of liquid flow sensors are also suitable for working with gases, which significantly expands the possibilities of using devices in industry and everyday life.
Types of liquid flow switches and their purpose
Modern types of fluid flow switches have a common main purpose - monitoring the presence or absence of working fluid flow in the pipeline. The differences lie in the operating principles and possibilities of using the sensors.
- Mechanical Paddle Flow Switch is a device built into a pipe, equipped with a special blade. If there is flow in the pipeline, the blade deflects, causing the contacts to close and trigger the sensor. The paddle relay has virtually no restrictions in use, is subject to little wear and does not require maintenance.
- Thermal flow switch monitors the presence of flow by measuring the level of thermal energy dissipation from the built-in heating element. Depending on the rate of change in the temperature of the heating element, the flow is recorded, as well as its speed if such a function is available. The hot-wire flow measuring principle is not suitable for some hazardous liquids. To maintain registration reliability, it is necessary to keep the sensor elements clean. Some types of devices are not suitable for operation in conditions of constantly changing flow rates.